With any old enlarger they will have picked up a certain amount of detritus over the years. It will be worth taking the head apart, cleaning out any dust that is present and giving the condensers a rub over too. Don't be frightened if you scratch them or if they are scratched already, that will not have the slightest effect on the image produced. If the bulb is looking 'tired' by which I mean any corrosion at the base or discolouration in the glass, change that too. I cannot remember if they had a small parabolic mirror at the back, that may also need a bit of cleaning as well as any heat absorbing glass which will be obvious